Reading Values With Sign Bits; Broken Transmitter Detection; Scaling And Converting The Input Data; Scaling The Input Data - Automation Direct DL405 User Manual

3–30
F4–04AD 4-Channel Analog Input
Reading Values
With Sign Bits
Broken Transmitter
Detection

Scaling and Converting the Input Data

Scaling the
Input Data
If the 13-bit magnitude plus sign format is selected, the sign bits (X44 to X47 in our
example) will be on when the corresponding analog input channel(s) send negative
data. The bits are always off (0000) in the 12-bit magnitude and two's complement
formats.
When the 4 to 20mA with broken transmitter detection range is selected, the four
Broken Transmitter bits (X50 to X53 in our example) will be on when the current on
the corresponding analog input channel(s) is below the normal 4 mA bottom end of
the range. The threshold at which these bits turn on is +1.25 mA.
The following examples show you how to scale and convert the input data, for both
16 Input and 32 Input modes.
Most applications usually
measurements in engineering units,
which provide more meaningful data.
This is accomplished by using the
conversion formula shown.
You may have to make adjustments to
the formula depending on the scale you
choose for the engineering units.
For example, if you wanted to measure pressure (PSI) from 0.0 to 99.9 then you
would have to multiply the analog value by 10 in order to imply a decimal place when
you view the value with the programming software or a handheld programmer.
Notice how the calculations differ when you use the multiplier.
Analog Value of 2024, slightly less than half scale, should yield 49.4 PSI
Example without multiplier
Units + A H * L
4095
Units + 2024 100 * 0
4095
Units + 49
Handheld Display
V 3101 V 3100
V MON 0000
require
Units + A H * L
H = high limit of the engineering
L = low limit of the engineering
A = analog value (0 – 4095)
Example with multiplier
Units + 10A H * L
Units + 20240 100 * 0
Units + 494
0049 V MON 0000
This value is more accurate
4095
unit range
unit range
4095
4095
Handheld Display
V 3101 V 3100
0494